/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.spark.util.collection.unsafe.sort;

import org.apache.spark.unsafe.Platform;
import org.apache.spark.unsafe.array.LongArray;
import org.apache.spark.unsafe.memory.MemoryBlock;
import org.apache.spark.util.collection.SortDataFormat;

/**
 * Supports sorting an array of (record pointer, key prefix) pairs.
 * Used in {@link UnsafeInMemorySorter}.
 *
 * Within each long[] buffer, position {@code 2 * i} holds a pointer pointer to the record at
 * index {@code i}, while position {@code 2 * i + 1} in the array holds an 8-byte key prefix.
 */
final class UnsafeSortDataFormat extends SortDataFormat<RecordPointerAndKeyPrefix, LongArray> {

    public static final UnsafeSortDataFormat INSTANCE = new UnsafeSortDataFormat();

    private UnsafeSortDataFormat() { }

    @Override
    public RecordPointerAndKeyPrefix getKey(LongArray data, int pos) {
        // Since we re-use keys, this method shouldn't be called.
        throw new UnsupportedOperationException();
    }

    @Override
    public RecordPointerAndKeyPrefix newKey() {
        return new RecordPointerAndKeyPrefix();
    }

    @Override
    public RecordPointerAndKeyPrefix getKey(LongArray data, int pos, RecordPointerAndKeyPrefix reuse) {
        reuse.recordPointer = data.get(pos * 2);
        reuse.keyPrefix = data.get(pos * 2 + 1);
        return reuse;
    }

    @Override
    public void swap(LongArray data, int pos0, int pos1) {
        long tempPointer = data.get(pos0 * 2);
        long tempKeyPrefix = data.get(pos0 * 2 + 1);
        data.set(pos0 * 2, data.get(pos1 * 2));
        data.set(pos0 * 2 + 1, data.get(pos1 * 2 + 1));
        data.set(pos1 * 2, tempPointer);
        data.set(pos1 * 2 + 1, tempKeyPrefix);
    }

    @Override
    public void copyElement(LongArray src, int srcPos, LongArray dst, int dstPos) {
        dst.set(dstPos * 2, src.get(srcPos * 2));
        dst.set(dstPos * 2 + 1, src.get(srcPos * 2 + 1));
    }

    @Override
    public void copyRange(LongArray src, int srcPos, LongArray dst, int dstPos, int length) {
        Platform.copyMemory(
                src.getBaseObject(),
                src.getBaseOffset() + srcPos * 16,
                dst.getBaseObject(),
                dst.getBaseOffset() + dstPos * 16,
                length * 16);
    }

    @Override
    public LongArray allocate(int length) {
        assert (length < Integer.MAX_VALUE / 2) : "Length " + length + " is too large";
        // This is used as temporary buffer, it's fine to allocate from JVM heap.
        return new LongArray(MemoryBlock.fromLongArray(new long[length * 2]));
    }

}
